Fabrication of doughnut-shaped particles from spheroidal paramylon granules of Euglena gracilis using acetylation reaction

A review of paramylon processing routes from microalga biomass to non-derivatized and chemically modified products

Paramylon is a linear β-1,3-glucan, similar to curdlan, produced as intracellular granules by the microalga Euglena gracilis, a highly versatile and robust strain, able to grow under various trophic conditions, with valorization of CO_2, wastewaters, or food byproducts as nutrients. This review focuses in particular on the various processing routes leading to new potential paramylon based products. Due to its crystalline structure, involving triple helices stabilized by internal intermolecular hydrogen bonds, paramylon is neither water-soluble nor thermoplastic. The few solvents able to disrupt the triple helices, and to fully solubilize the polymer as random coils, allow non derivatizing shaping into films, fibers, and even nanofibers by a specific self-assembly mechanism. Chemical modification in homogeneous or heterogeneous conditions is also possible. The non-selective or regioselective substitution of the hydroxyl groups of glucosidic units leads to water-soluble ionic derivatives and thermoplastic paramylon esters with foreseen applications ranging from health to bioplastics.

Thermal, crystalline, and pressure-sensitive adhesive properties of paramylon monoesters derived from an euglenoid polysaccharide

The thermal, crystalline, and pressure-sensitive adhesive properties of thermoplastic monoesters made from paramylon, a storage polysaccharide of Euglena gracilis, and a long-chain acyl chloride, were examined. Differential scanning calorimetry revealed that the thermal properties of these paramylon monoesters were dependent on the chain length and the average degree of substitution of the long-chain acyl group (av. DS_lca). X-ray diffractometry revealed that the product solids with a myristoyl or palmitoyl group had a less ordered lateral acyl chain structure than those with a stearoyl group. Tackiness testing showed that the introduction of a myristoyl group into paramylon with an av. DS_lca of ∼2.6 to ∼2.9 yielded palpable pressure-sensitive adhesion. A slight deviation of the chain length and/or av. DS_lca from those of tacky paramylon myristate solids weakened or dispersed the tackiness. These results demonstrate the feasibility of using paramylon myristate solids with the av. DS_lca in a specific range as a practical pressure-sensitive adhesive.

Biosynthesis of silver nanoparticles using Euglena gracilis, Euglena intermedia and their extract

Extracellular and intracellular biosynthesis of silver nanoparticles (AgNPs) by Euglena gracilis (EG) strain and Euglena intermedia (EI) strain are reported in this study. The obtained nanoparticles showed an absorption peak approximates 420 nm in the UV-visible spectrum, corresponding to the plasmon resonance of AgNPs. According to the result of inductively coupled plasma-atomic emission spectrometer, the intakes of silver ions by EI and EG are roughly equal. The transmission electron microscope (TEM) analysis of the successful in vivo and in vitro synthesised AgNPs indicated the sizes, ranging from 6 to 24 nm and 15 to 60 nm in diameter, respectively, and a spherical-shaped polydispersal of the particles. The successful formation of AgNPs has been confirmed by energy dispersive X-ray analysis connected to the TEM. The Fourier transform infrared spectroscopy measurements reveal the presence of bioactive functional groups such as amines are found to be the capping and stabilising agents of nanoparticles. To our knowledge, this is the first report where two kinds of Euglena microalga were used as the potential source for in vivo and in vitro biosynthesis of AgNPs.

Euglenoid flagellates: a multifaceted biotechnology platform

Euglenoid flagellates are mainly fresh water protists growing in highly diverse environments making them well-suited for a multiplicity of biotechnology applications. Phototrophic euglenids possesses complex chloroplasts of green algal origin bounded by three membranes. Euglena nuclear and plastid genome organization, gene structure and gene expression are distinctly different from other organisms. Our observations on the model organism Euglena gracilis indicate that transcription of both the plastid and nuclear genome is insensitive to environmental changes and that gene expression is regulated mainly at the post-transcriptional level. Euglena plastids have been proposed as a site for the production of proteins and value added metabolites of biotechnological interest. Euglena has been shown to be a suitable protist species to be used for production of several compounds that are used in the production of cosmeceuticals and nutraceuticals, such as α-tocopherol, wax esters, polyunsaturated fatty acids, biotin and tyrosine. The storage polysaccharide, paramylon, has immunostimulatory properties and has shown a promise for biomaterials production. Euglena biomass can be used as a nutritional supplement in aquaculture and in animal feed. Diverse applications of Euglena in environmental biotechnology include ecotoxicological risk assessment, heavy metal bioremediation, bioremediation of industrial wastewater and contaminated water.

Thermoplasticization of euglenoid β-1,3-glucans by mixed esterification

We experimentally demonstrated that paramylon, a storage polysaccharide of Euglena gracilis, is efficiently thermoplasticized by adding acyl groups that differ in alkyl chain length. Glass transition temperature of mixed paramylon esters was higher than those of plant-based polylactic acid (PLA), poly 11-aminoundecanoic acid (PA11), and petroleum-based acrylonitrile-butadiene-styrene (ABS) resin and was comparable to that of cellulose acetate stearate (CAS). Their thermoplasticity was equivalent to or higher than those of these reference plastics. The bending strength and bending elastic modulus of injection molded test specimens made from mixed paramylon esters were comparable to those of the reference plastics. While their impact strength was lower than that of specimens made from ABS resin and CAS, it was comparable to those of PLA and PA11. Euglenoid β-1,3-glucans are thus a potential component of thermoplastic materials.

Preparation of carboxylic acid-bearing polysaccharide nanofiber made from euglenoid β-1,3-glucans

This paper introduces a new strategy for creating surface modified polysaccharide nanofibers. To demonstrate proof of principle, the synthesis, structure, and self-assembly behavior of a carboxylic acid-bearing polysaccharide made from paramylon (β-1,3-glucan) and succinic anhydride were investigated. Examination by a combination of NMR, FT-IR, and SEC-MALLS confirmed that successful preparation of the desired succinylated paramylon without significant depolymerization. NMR, SEC-MALLS, visible absorption and CD spectroscopic analyses indicated that the paramylon derivative forms the triplex structure in solutions. SEM observation revealed that succinylated paramylon forms a nanofiber that has carboxylic acid on the surface.

Polysaccharide nanofiber made from euglenoid alga

We have fabricated a polysaccharide nanofiber made from paramylon (β-1,3-glucan), a storage polysaccharide stored as a micrometer-sized particle in the cell of euglenoid alga. Preparation of this nanofiber primarily hinges on the bottom-up approach. First, paramylon, which is originally present in the form of a bundle of nanofibers in a particle, was fibrillated to a randomly coiled polymer by dissolving the particle in a 1.0-mol/L NaOH aqueous solution. Second, the randomly coiled polymer was allowed to self-assemble into a triplex as the NaOH concentration was reduced to 0.25-0.20mol/L. Third, a 20-nm-width nanofiber made from the triplex emerged in the solution when the NaOH concentration was reduced to approximately 0.20mol/L.